Syntheses, structures, and catalytic activity in Friedel–Crafts acylations of substituted tetramethylcyclopentadienyl molybdenum carbonyl complexes

Article abstract of DOI:10.1007/s11243-018-0217-5

Reactions of the substituted tetramethylcyclopentadienes [C₅HMe₄R] [R?=?^tBu, Ph, CH₂CH₂C(CH₃)₃] with Mo(CO)₃(CH₃CN)₃ in refluxing xylene gave a series of dinuclear molybdenum carbonyl complexes [(η⁵-C₅Me₄R)Mo(CO)₃]₂ [R?=?^tBu (1), Ph (2), CH₂CH₂C(CH₃)₃ (3)], [(η⁵-C₅Me^tBu)Mo(μ-CO)₂]₂ (4)], and [(η⁵-C₅Me₄)^tBu]₂Mo₂O₄(μ-O) (5)], respectively. Complexes 1–5 were characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectroscopy. In addition, their crystal structures were determined by X-ray crystal diffraction analysis. The catalytic activities of complexes 1–3 in Friedel–Crafts acylation in the presence of o-chloranil has also been investigated; the reactions were achieved under mild conditions to give the corresponding products in moderate yields.

Full text of DOI:10.1007/s11243-018-0217-5

Transition Metal Chemistry
https://doi.org/10.1007/s11243-018-0217-5
Syntheses, structures, and catalytic activity in Friedel–Crafts
acylations of substituted tetramethylcyclopentadienyl molybdenum
carbonyl complexes
1
1
1
2
3
1
1
1
Tong Li · Xin‑Long Yan · Zhan‑Wei Li · Zhi‑Hong Ma · Su‑Zhen Li · Zhan‑Gang Han · Xue‑Zhong Zheng · Jin Lin
Received: 12 November 2017 / Accepted: 9 February 2018
©
Springer International Publishing AG, part of Springer Nature 2018
Abstract
t
Reactions of the substituted tetramethylcyclopentadienes [C HMe R] [R = Bu, Ph, CH CH C(CH ) ] with
5
4
2
2
3 3
5
Mo(CO) (CH CN) in reꢀuxing xylene gave a series of dinuclear molybdenum carbonyl complexes [(η -C Me R)Mo(CO) ]
3
3
3
5
4
3 2
t
5
t
5
t
[
R = Bu (1), Ph (2), CH CH C(CH ) (3)], [(η -C Me Bu)Mo(μ-CO) ] (4)], and [(η -C Me ) Bu] Mo O (μ-O) (5)], respec-
2
2
3 3
5
2 2
5
4
2
2
4
1
13
tively. Complexes 1–5 were characterized by elemental analysis, IR, H NMR, and C NMR spectroscopy. In addition,
their crystal structures were determined by X-ray crystal diꢁraction analysis. The catalytic activities of complexes 1–3 in
Friedel–Crafts acylation in the presence of o-chloranil has also been investigated; the reactions were achieved under mild
conditions to give the corresponding products in moderate yields.
Introduction
new compounds, but also have great inꢀuence on the metal-
locene catalytic activity [7, 8].
Transition metal complexes are of considerable utility as
catalysts in organic synthesis [1–6]. The ligands usually play
a crucial role in the catalytic processes by ꢂne-tuning the
electronic and geometric properties of the complex. Cyclo-
pentadienyls have been among the most important ligands in
organo-transition metal chemistry, as they form a wide range
of derivatives whose steric and electronic properties can be
easily tailored by varying the ring substituents. These vari-
ations on the cyclopentadienyl unit not only open access to
The Friedel–Crafts reaction is well known and widely
used for the production of value-added aromatic compounds
through the formation of new C–C bonds. Conventional
Friedel–Crafts alkylations are catalyzed by Lewis and Brön-
sted acids. However, the separation and handling of the acid
waste in these homogeneous processes raise undesirable eco-
nomic, environmental, and safety issues [9–18]. Therefore,
considerable eꢁort has been devoted to the development of
environmentally friendly alternatives. Our laboratory has
been pursuing the development of new ecofriendly catalyst
systems. The activities and selectivities of diꢁerent catalysts
have been evaluated in our laboratory with a view to the
development of green Friedel–Crafts acylation and alkyla-
tion reactions [19–24]. To obtain a deeper insight into the
steric and electric eꢁects of substituents on the molecular
structures and reactions of the corresponding biscyclopen-
tadienyl binuclear metal carbonyl complexes, we have now
prepared a series of biscyclopentadienyl dimolybdenum
complexes and determined their structures. The catalytic
activities of the dinuclear molybdenum carbonyl complexes
for Friedel–Crafts acylation have been investigated in the
presence of o-chloranil as the oxidant. The results of our
studies are presented in this paper.
Tong Li, Xin-Long Yan, and Zhan-Wei Li have contributed
equally to this work.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11243-018-0217-5) contains
supplementary material, which is available to authorized users.
*
Zhi-Hong Ma
mazhihong-1973@163.com
*
Jin Lin
linjin64@126.com
1
2
3
The College of Chemistry and Material Science, Hebei
Normal University, Shijiazhuang 050024, China
School of Pharmacy, Hebei Medical University,
Shijiazhuang 050017, China
Hebei College of Industry and Technology,
Shijiazhuang 050091, China
Vol.:(0
1
123456789)
3

Transition Metal Chemistry
Experimental
Synthesis of complex (3)
General considerations
Using a procedure similar to that described
above, C HMe CH CH C(CH ) was reacted with
5
4
2
2
3 3
All reactions were carried out under an argon/vacuum
manifold using standard Schlenk techniques, except where
noted otherwise. Solvents were distilled from appropriate
Mo(CO) (CH CN) in reꢀuxing xylene for 48 h. After
3 3 3
chromatography and elution with petroleum ether,
5
[(η -C Me CH CH C(CH ) )]Mo(CO) ] (3) was
5
4
2
2
3
3
3 2
1
13
drying agents under a dry argon atmosphere. H and
C
obtained (0.49 g, 31.7% yield) as dark red crystals. M.P.
NMR spectra were recorded on Bruker AV 500 or WIPM-
135.4–135.8 °C; Anal. Calcd for C H Mo O : C, 56.11;
3
6
50
2
6
1
NMR-400 spectrometers in CDCl , while IR spectra were
H, 6.54. Found (%): C, 56.33; H, 6.56; H NMR (CDCl ,
3
3
recorded as KBr disks on an IR FT 8900 spectrometer. Gas
chromatography was performed with an Agilent 6820 gas
chromatography instrument. Mass spectra were recorded
on a DSQ(II) gas chromatograph–mass spectrometer. The
500 MHz): δ 0.92 (s, 18H, CH ), 1.14–1.18 (m, 4H, CH ),
3
2
1
3
1.94(s, 24H, C Me ), 2.27–2.31 (m, 4H, CH ); C NMR
5
4
2
(CDCl , 125 MHz):δ 10.4, 10.7, 21.0, 29.0, 30.6, 44.8,
3
−
1
104.0, 105.1, 109.4, 235.5. IR(υ , KBr, cm ): 1921(s),
CO
t
proligands [C Me HR] [R = Bu, Ph, CH CH C(CH ) ]
1888(s), 1871(s).
5
4
2
2
3 3
were prepared as described in the literature [25, 26].
Mo(CO) (CH CN) was synthesized according to the lit-
3
3
3
Synthesis of complex (4)
erature procedure [27].
Using a procedure similar to that described above,
t
C HMe Bu was reacted with Mo(CO) (CH CN) in reꢀux-
5
4
3
3
3
Synthesis of complex (1)
ing xylene for 12 h. After chromatography and elution with
5
t
5
t
petroleum ether, [(η -C Me Bu)Mo(CO) Mo(η -C Me Bu)]
5
4
5
4
t
Under an argon atmosphere, a solution of C HMe Bu
5
4
(4) was obtained (0.61 g, 46.9% yield) as dark red crys-
(
0.708 g, 4 mmol) and Mo(CO) (CH CN) (2 mmol) in
3 3 3
tals. M.P. 166.7–167.5 °C; Anal. Calcd for C H Mo O :
3
0
42
2
4
1
xylene (30 mL) was reꢀuxed for 4 h. After removal of solvent,
the residue was loaded onto an alumina column. Upon elu-
C, 54.72; H, 6.42. Found (%): C, 54.67; H, 6.10; H NMR
(
CDCl , 500 MHz): δ 1.92 (s, 12H, C Me ), 2.04 (s, 12H,
3 5 2
t
13
tion with petroleum ether/CH Cl (10:1), a brown band was
2
2
C Me ), 1.37(s, 18H, Bu); C NMR (CDCl , 125 MHz):
5 2 3
5
t
collected. After concentration, [(η -C Me Bu)Mo(CO) ] (1)
5
4
3 2
δ 10.3, 13.4, 32.7, 34.5, 102.8, 105.5, 115.7. IR (υ , KBr,
CO
−
1
was aꢁorded as brown crystals. Yield: 36.8% (0.263 g). M.P:
cm ): 1867(s), 1826(s).
1
74.9–175.8 °C; Anal. Calcd for C H Mo O : C, 53.78;
3
2
42
2
6
1
H, 5.92. Found (%): C, 53.98; H, 5.94; H NMR (CDCl ,
3
Synthesis of complex (5)
4
00 MHz): δ 1.44 (s, 18H, CH ), 1.81(s, 12H, C Me ), 2.14
3 5 4
13
(
s, 12H, C Me ); C NMR (CDCl , 101 MHz): δ 11.2, 14.3,
5 4 3
t
−
1
A solution of C HMe Bu (0.708 g, 4 mmol) and
5
4
3
2.5, 35.2, 102.1, 110.8, 114.9, 235.9. IR(υ , KBr, cm ):
CO
Mo(CO) (CH CN) (2 mmol) in xylene (20 mL) was
3
3
3
1
926(s), 1889(s), 1870(s).
reꢀuxed for 12 h under air. After chromatography and elu-
5
t
tion with petroleum ether, [(η -C Me ) Bu] Mo O (μ-O)] (5)
5
4
2
2
4
was obtained (0.346 g, 27.6% yield) as dark red crystals.
Synthesis of complex (2)
M.P. 159.6–160.5 °C; Anal. Calcd for C H Mo O : C,
2
6
42
2
5
1
4
4
1
1
9.85; H, 6.76. Found: C, 50.05; H, 6.78; H NMR (DMSO,
Using a procedure similar to that described above,
C HMe Ph was reacted with Mo(CO) (CH CN) in reꢀux-
00 MHz): δ 1.89 (s, 12H, C Me ), 2.13 (s, 12H, C Me ),
5
2
5
2
5
4
3
3
3
t
13
.29 (s, 18H, C Bu); C NMR (DMSO, 101 MHz): δ 10.8,
5
ing xylene for 48 h. After chromatography and elution
−1
4.3, 31.6, 35.6, 122.1, 124.8, 127.4; IR (KBr, cm ): 908
5
with petroleum ether, [(η -C Me Ph)Mo(CO) ] (2) was
5
4
3 2
w, 878 w (υ
), 761 w (υ
).
Mo–O–Mo
Mo=O
obtained (0.38 g, 28.6% yield) as dark red crystals. M.P.
1
36.3–137.0 °C; Anal. Calcd for C H Mo O : C, 57.31;
36 34 2 6
1
Crystallographic studies
H, 4.54. Found (%): C, 56.87; H, 4.15; H NMR (CDCl ,
3
5
7
9
2
00 MHz): δ 1.92 (s, 12H, C Me ), 2.01 (s, 12H, C Me ),
5 2 5 2
1
3
Single crystals of complexes 1–5 suitable for X-ray diꢁrac-
tion were obtained from the slow evaporation of hexane-
dichloromethane solutions. All X-ray crystallographic data
were collected on a Bruker AXS SMART 1000 CCD dif-
fractometer, using graphite monochromated Mo Kα radiation
.28–7.36 (m, 10H, C H ); C NMR (CDCl , 101 MHz): δ
6
5
3
.9, 10.6, 103.5, 104.9, 109.6, 127.2, 128.0, 131.4, 132.9,
−
1
38.8. IR(υ , KBr, cm ): 1869(s), 1822(s).
CO
1
3

Transition Metal Chemistry
Table 1 Crystal data and structure reꢂnement parameters for complexes 1–5
Complex
1
2
3
4
5
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system,
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C H Mo O
714.54
298 (2)
0.71073
Triclinic
P − 1
C H MoO
377.26
298 (2)
0.71073
Triclinic
Pī
8.8032 (7)
9.0574 (8)
11.7046 (9)
111.183 (3)
107.893 (2)
90.9170(10)
819.58 (12)
2
C H Mo O
770.64
298 (2)
0.71073
Monoclinic
P2(1)/c
8.9750 (8)
16.2189 (14)
12.7041 (11)
90
91.0220 (10)
90
1849.0 (3)
4
C H Mo O
658.51
298 (2)
0.71073
C H Mo O
5
626.48
298 (2)
0.71073
Monoclinic
P2(1)/n
8.3263 (17)
10.523 (2)
15.401 (3)
90
99.667 (2)
90
1330.3 (5)
2
3
2
42
2
6
18 17
3
36 50
2
6
30 42
2
4
26 42
2
Monoclinic
P2 /n
1
8.7635 (8)
8.3600 (15)
22.228 (4)
15.872 (3)
90
92.452 (2)
90
2946.7 (9)
4
1.484
12.0465 (12)
15.9764 (14)
84.536 (2)
87.952 (2)
69.8520 (10)
1576.2 (3)
2
1.506
0.836
732
γ (°)
3
Volume (Å )
Z
Dcalc (g cm−3)
1.529
0.809
382
1.384
0.718
796
1.564
0.975
644
−
1
μ (mm
F(000)
)
0.883
1352
Crystal size(mm)
θ range (°)
Reꢀections collected
R (int)
0.18 × 0.17 × 0.14
2.48–25.02
8042/5485
0.0210
0.40 × 0.37 × 0.26
2.44–25.02
4157/2832
0.0557
0.38 × 0.17 × 0.15
2.51–25.02
9148/3247
0.0333
0.45 × 0.44 × 0.40
2.57–25.02
14,627/5173
0.0296
0.20 × 0.15 × 0.14
2.35–25.01
6494/2348
0.0211
Completeness to θ (%)
Absorption correction
Max. and min. transmission
Reꢂnement method
Data/restraints/parameters
Goodness-of-ꢂt on F2
R , wR [I > 2σ(I)]
98.4
98.10
99.3
97.2
100.0
Semi-empirical from equivalents
0.8919/0.8641
Full-matrix least-squares on F
5485/0/361
1.021
0.0342, 0.0851
0.0500, 0.0899
0.584
− 0.394
1,574,536
0.8132/0.7379
0.8999/0.7720
0.7191/0.6922
0.8755/0.8288
2
2832/0/203
1.073
0.0578, 0.1556
0.0633, 0.1642
1.060
− 0.826
1,555,752
3247/0/206
1.072
0.0321, 0.0636
0.0564, 0.0742
0.784
− 0.477
1,559,899
5173/3/410
1.078
0.0435, 0.1010
0.0787, 0.1257
0.748
− 1.566
1,556,542
2348/0/158
1.309
0.0253, 0.0603
0.0364, 0.0668
0.504
− 0.336
1,565,792
1
2
R , wR (all data)
1
2
−
3
Max. peak/(e Å
Mini. peak/(e Å
CCDC
)
−
3
)
(
φ/ω scan, λ = 0.71073 Å). Semiempirical absorption cor-
were mixed with 1,2-dichloroethane (3.5 mL) in a 25 mL
round-bottom ꢀask at room temperature. The solution
was immediately darkened. After stirring for 40 min at
room temperature, the aromatic compound (2 mmol) and
acylating reagent (6 mmol) were added by syringe. The
reaction mixture was then heated on an oil bath at 80 °C
for 24 h. After cooling to room temperature, the solvent
was removed through rotary evaporation. The residue was
puriꢂed by Al O column chromatography. Elution with
rections were applied for all complexes. The structures were
solved by direct methods and reꢂned by full-matrix least-
squares. All calculations were done using the SHELXL-97
program system. Crystallographic data and experimental
details of the structure determinations are given in Table 1.
CCDC: 1574536, 1555752, 1559899, 1556542, and
1
565792 for 1–5, respectively. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; e-mail: deposit@ccdc.cam.ac.uk.
2
3
petroleum ether/ethyl acetate (4:1, V/V) developed a color-
less liquid that aꢁorded the corresponding product. The
course of the reaction was monitored using an Agilent
6820 gas chromatograph.
General procedure for catalytic tests
Under an argon atmosphere, the required molybdenum
carbonyl complex (0.2 mmol) and o-chloranil (0.8 mmol)
1
3

Transition Metal Chemistry
t
Results and discussion
When the proligand [C5HMe4Bu] was reacted with
Mo(CO) (CH CN) in refluxing xylene for 12 h under an
3
3
3
Reactions of proligands [C HMe R]
argon atmosphere, the unexpected Mo–Mo triple-bonded
5
4
5
t
5
t
with Mo(CO) (CH CN)
complex [(η -C5Me Bu)Mo(CO)4Mo(η -C5Me4Bu) (4)]
was obtained (Scheme 2). The IR spectrum of complex 4
showed characteristic strong absorption peaks for CO in
3
3
3
t
Treatment of the proligands [C HMe R] [R = Bu, Ph, or
5
4
1
CH CH C(CH ) ] with Mo(CO) (CH CN) in refluxing
the bridging v(CO) region, while the H NMR spectrum
2
2
3 3
3
3
3
xylene under argon aꢁorded the expected Mo–Mo single-
showed two singlets for the four methyl group protons and
5
bonded dinuclear complexes [(η -C Me R)Mo(CO) ]
one singlet for the t-butyl protons.
5
4
3 2
t
t
[
R = Bu (1), Ph (2), CH CH C(CH ) (3)] (Scheme 1).
However, when proligand [C5HMe4Bu] was reacted
2
2
3 3
Among the three reactions, the t-butyl-substituted proligand
gave the shortest reaction time and highest activity, indicat-
ing that the steric and electronic eꢁects of the substituent
have a signiꢂcant eꢁect on the reaction.
with Mo(CO)3(CH3CN)3 in reꢀuxing xylene for 12 h while
5
exposed to air, the dinuclear oxo-bridged complex [(η -
t
C5Me4) Bu]2Mo2O4(μ-O) (5)] was obtained (Scheme 3).
The IR spectrum of complex 5 shows three characteristic
−
1
The IR spectra of complexes 1–3 are similar; all show
peaks at 908, 878, and 761 cm , corresponding to the two
terminal Mo=O stretching modes and a bridging antisym-
−
1
strong terminal carbonyl absorptions at 1926–1822 cm .
1
1
The H NMR spectra of 1 and 2 are also similar, showing
metric Mo–O–Mo stretching mode, respectively. The H
1
two singlets for the four methyl group protons, while the H
NMR spectrum shows two singlets for the four methyl group
NMR spectrum of complex 3 shows one singlet for the four
methyl group protons.
protons and one singlet for the t-butyl protons.
In order to further study the effect of substituent
on the reaction, the reaction time for the reaction of
t
[
C HMe Bu] with Mo(CO) (CH CN) was extended.
5
4
3
3
3
R
CO
OC
CO
CO
xylene
reflux
Mo(CO) (CH CN)
3
Mo
Mo
R +
3
3
OC
R
CO
t
Scheme 1 Synthesis of complexes 1–3. R = Bu (1), Ph (2), CH CH C(CH ) (3)
2
2
3 3
O O
C C
xylene
reflux, 12h
But + Mo(CO) (CH CN)
But
3
3
3
But
Mo
Mo
C C
O O
Scheme 2 Synthesis of complex 4
Scheme 3 Synthesis of com-
plex 5
But
O
O
Mo(CO) (CH CN)
3
3
3
But
Mo O Mo
O , xylene, reflux, 12h
2
But
O
O
1
3

Transition Metal Chemistry
Table 2 Selected bond distances (Å) and angles (°) for complexes 1–5
1
2
3
4
5
Bond distances
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–C(4)
Mo(1)–C(5)
Mo(1)–C(14)
O(1)–C(14)
2.344 (4) Mo(1)–C(1) 2.329 (5) Mo(1)–C(1) 2.414 (3)
2.320 (4) Mo(1)–C(2) 2.326 (5) Mo(1)–C(2) 2.378 (3)
2.387 (4) Mo(1)–C(3) 2.385 (5) Mo(1)–C(3) 2.312 (3)
2.424 (4) Mo(1)–C(4) 2.423 (5) Mo(1)–C(4) 2.300 (3)
2.384 (4) Mo(1)–C(5) 2.380 (5) Mo(1)–C(5) 2.373 (4)
1.989 (5) Mo(1)–C(16) 1.958 (5) Mo(1)–C(16) 1.973 (4)
1.161 (5) Mo(1)–C(17) 1.996 (6) Mo(1)–C(17) 1.976 (5)
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–C(4)
Mo(1)–C(5)
Mo(1)–C(27)
Mo(2)–C(28)
O(1)–C(27)
2.338 (4) Mo(1)–C(1)
2.337 (5) Mo(1)–C(2)
2.355 (5) Mo(1)–C(3)
2.352 (5) Mo(1)–C(4)
2.326 (5) Mo(1)–C(5)
2.127 (13) Mo(1)–O(1)
2.072 (10) Mo(1)–O(2)
1.232 (12) Mo(1)–O(3)
2.361 (3)
2.451 (3)
2.481 (3)
2.475 (3)
2.430 (3)
1.8933 (4)
1.704 (2)
1.705 (2)
Mo(1)–
3.3352 (7) O(1)–C(16)
1.157 (7) O(1)–C(16)
1.152 (4)
Mo(1i)
Mo(2)–
Mo(2i)
3.3398 (7) Mo(1)–
Mo(1i)
3.309
Mo(1)–
Mo(1i)
3.279
Mo(1)–Mo(2) 2.4775 (7) O(1)–Mo(1i)
1.8933 (4)
Bond angles
C(2)–Mo(1)–
36.36 (12) C(2)–Mo(1)– 36.19 (17) C(2)–Mo(1)– 34.55 (11) C(2)–Mo(1)–
C(1) C(1) C(1)
34.30 (12) C(3)–Mo(1)– 34.60 (17) C(3)–Mo(1)– 36.11 (12) C(3)–Mo(1)–
C(4) C(4) C(4)
35.85 (17) C(2)–Mo(1)–
C(1)
34.99 (9)
33.37 (10)
56.84 (9)
105.38(9)
C(1)
C(3)–Mo(1)–
C(4)
34.60 (18) C(3)–Mo(1)–
C(4)
C(1)–Mo(1)–
59.21 (12) C(1)–Mo(1)– 59.00 (18) C(1)–Mo(1)– 58.24 (11) C(1)–Mo(1)–
59.27 (16) C(1)–Mo(1)–
C(3)
C(3)
C(3)
C(3)
C(3)
C(15)–
Mo(1)–
C(14)
77.45 (19) C(16)–
77.0 (2)
C(16)–
Mo(1)–
C(17)
77.85 (15) C(27)–
118.7 (5) O(2)–Mo(1)–
Mo(1)–
Mo(1)–
O(1)
C(17)
C(29)
C(15)–
Mo(1)–
C(16)
76.3 (2) C(16)–
77.5 (2)
C(16)–
Mo(1)–
C(18)
77.34(16)
C(28)–
Mo(2)–
C(29)
83.8(5) O(2)–Mo(1)– 105.78 (14)
O(3)
Mo(1)–
C(18)
C(16)–
Mo(1)–
C(14)
112.09 (19) C(18)–
110.0 (2) C(18)–
Mo(1)–
C(17)
111.93 (15) C(28)–
Mo(2)–
Mo(1)
68.8 (3) Mo(1)–O(1)– 180.000 (15)
Mo(1i)
Mo(1)–
C(17)
Crystal structures
form in solution; however, the possibility of a rapid ꢀuxional
process cannot be excluded. For complex 2, the conforma-
tion of the phenyl substituent is found to be a regular hexa-
gon. The structural parameters of complexes 1–3 are very
The crystal structures of complexes 1–5 were determined
by X-ray diꢁraction. Selected bond parameters for these
complexes are presented in Table 2. The structures of
complexes 1–3 are shown in Figs. 1, 2, and 3. All three
complexes consist of two (C Me R)Mo(CO) units, in
5
similar to those in other [η -C H RMo(CO) ] complexes;
5
4
3 2
the Mo–Mo bond distances are [3.3352 (7) and 3.3398 (7) Å
for complex (1)], 3.309 Å for (2) and 3.279 Å for (3), which
are comparable to other metal–metal bond distances found
5
4
3
which each of the molybdenum atoms is coordinated with
5
5
an η -cyclopentadienyl and three terminal CO ligands. All
in this kind of [η -C Me RMo(CO) ] complex [R = PhMe,
5
4
3 2
the complexes are disposed in the trans conformation and
linked by an Mo–Mo bond, such that the structures lie on
a crystallographic inversion. Two structurally independ-
ent but chemically equivalent molecules are present in the
unit cell. The ꢂfth coordination position is occupied by a
cyclopentadienyl ring that is essentially planar. For com-
plex 1, the unit cell contains two environmentally diꢁerent
molecules Mo(1) and Mo(2), which have the same basic
structure, but small diꢁerences in some bond lengths and
angles. The Mo–Mo distances are 3.3352 (7) and 3.3398
(3.283 Å); R = PhOMe (3.307 Å) [28]; R = benzyl (3.266 Å
[29]; R = n-butyl (3.286 Å) [30]]. However, the Mo–Mo
bond distances for complexes 1–3 are longer than those
5
reported for trans-[η -C H Mo(CO) ] [3.235(1) Å] [31]
5
5
3 2
5
i
and [η -C H PrMo(CO) ] [3.222(5) Å] [32], suggesting that
5
4
3 2
the substituents of the cyclopentadienyl ring have diꢁerent
degrees of steric hindrance.
The molecular structure of complex 4 is shown in
Fig. 4. The molecule consists of two t-butyl-substituted
tetramethylcyclopentadienyl molybdenum moieties sym-
metrically bridged by four carbonyls. Complex 4 is a cis-
dimolybdenum complex, in which every molybdenum
(
7) Å, respectively. Although there are two distinct mol-
1
ecules in the unit cell, the H NMR spectrum of 1 shows
only one. This indicates that complex 1 may exist as one
5
atom is coordinated by an η -cyclopentadienyl and four
1
3

Transition Metal Chemistry
Fig. 1 Molecular structure of 1 with atom numbering scheme. Thermal ellipsoids are shown at the 30% level. Hydrogen atoms are omitted for
clarity. Mo1–Mo1i = 3.3352(7) Å, Mo2–Mo2ii = 3.3398(7) Å
Fig. 2 Molecular structure of 2
with atom numbering scheme.
Thermal ellipsoids are shown at
the 30% level. Hydrogen atoms
are omitted for clarity. Mo1–
Mo1i = 3.309 Å
bridging carbonyl ligands. According to the EAN formal-
ism, a triple Mo–Mo bond must be formulated, which is in
agreement with the very short intermetallic length, 2.4777
having four carbonyl ligands bridging a triple metal–metal
bond discovered in our laboratory.
The molecular structure of complex 5 is shown in Fig. 5.
Complex 5 is a pentaoxo dimer and crystallizes in the mon-
oclinic space group P2(1)/n. The molecule contains two
molybdenum atoms connected with a single oxygen bridge.
The two cyclopentadienyl planes are parallel. The complex
is centrosymmetric with a Mo(1)–O(1)–Mo(1i) angle of
180°; the Mo(1)–O(1)–Mo(1i) moiety is collinear. This lin-
ear arrangement is attributed to π-bonding after the possible
consequences of steric interactions are considered. In fact, a
(
8) Å, ca. 0.8 Å shorter than the corresponding distance
in the electron-precise complexes 1–3 and similar to the
values found for related triply bonded cyclopentadienyl
complexes bridged by dialkyl- or diarylphosphide ligands
such as [Mo Cp (µ-COEt)–(µ-PCy )(µ-CO)] (2.478(1) Å)
2
2
2
[
[
33], [Mo Cp (µ-PPh ) (µ-CO)] (2.515(2) Å) [34], and
2 2 2 2
Mo Cp (µ-PhPC H PPh) (µ-CO)] (2.532(1) Å) [35]. We
2
2
6
4
2
should note that complex 4 is the ꢂrst example of a complex
1
3

Transition Metal Chemistry
Fig. 3 Molecular structure of 3
with atom numbering scheme.
Thermal ellipsoids are shown at
the 30% level. Hydrogen atoms
are omitted for clarity. Mo1–
Mo1i = 3.279 Å
Fig. 4 Molecular structure of 4
with atom numbering scheme.
Thermal ellipsoids are shown at
the 10% level. Hydrogen atoms
are omitted for clarity
linear, centrosymmetric arrangement in a [(MoO ) O] unit
Mo(1i)–O(1) are identical [1.8933 (4) Å], while the terminal
Mo=O distances (average 1.7045 Å) are much longer than
2
2
5
has been previously observed in [(η -C Me )MoO ] (μ-O)
5
5
2 2
5
[
36]. In complex 5, the bond distances of Mo(1)–O(1) and
those in [(η -C Me )MoO ] (μ-O) (average 1.67 Å)]. The
5
5
2 2
1
3

Transition Metal Chemistry
Fig. 5 Molecular structure of 5
with atom numbering scheme.
Thermal ellipsoids are shown at
the 30% level. Hydrogen atoms
are omitted for clarity
R1
R1
O
O
Cat.(10.0 mol%)/ o-Chloranil (40.0mol%)
+
R2
Cl
ClCH CH Cl (3.5 mL), 80
R2
2
2
2
mmol
6 mmol
Scheme 4 Complexes 1–3/o-chloranil-catalyzed Friedel–Crafts acylation reactions of toluene/anisole with acyl chlorides. R = OCH (6),
1
3
CH (7); R = Ph (a), PhCH (b), c-C H (c), n-C H (d), PhCH=CH (e)
3
2
2
6
11
5
11
OMe
OMe
R1
R2
+
O
O
R2
Cat.(10.0 mol%)/ o-Chloranil (40.0mol%)
R3
Cl
R3
ClCH CH Cl (3.5 mL), 80
2
2
R1
mmol
2
6 mmol
Scheme 5 Complexes 1–3/o-chloranil-catalyzed Friedel–Crafts acylation reactions of anisole derivatives with acyl chlorides. R = H;
1
R = CH (8), Br(9). R = CH (10), Br(11); R = H. R = Ph (a), PhCH (b), c-C H (c), n-C H (d), PhCH=CH (e)
2
3
1
3
2
3
2
6
11
5
11
long bond distances of terminal Mo=O bonds have been
suggested to decrease O–O repulsion and result in O–Mo–O
angles larger than 90°.
considerations were initially considered. The inꢀuence of
quinones on catalytic eꢃcacy has been discussed by Yama-
moto et al. [37]. o-Chloranil was identiꢂed as the best oxi-
dant. The optimized experimental conditions were as fol-
lows: 1,2-dichloroethane as solvent; a molar ratio 1:3 of
aromatic substrate and acylation reagent; the amount of
catalyst was 10 mol% (substrate as reference); the molar
ratio of catalyst to oxidant was 1:4; reaction temperature
80 °C, reaction time 24 h.
Catalytic studies
In order to test the ability of these complexes to catalyze
Friedel–Crafts acylation reactions (Schemes 4, 5), inꢀuenc-
ing factors such as the reaction time, yield, and economic
1
3

Transition Metal Chemistry
Table 3 Catalytic data of
complexes 1–3
Aromatic substrate
PhMe
Reagent
PhCOCl
Yield [%] cata-
Yield [%] cata-
Yield [%]
catalyzed
by 3
lyzed by 1
lyzed by2
56.5
44.8
–
28.3
–
58.7
45.6
–
30.8
–
55.2
45.1
31.5
–
PhCH COCl
2
n-C H COCl
5
11
c-C H COCl
6
11
PhCH=CHCOCl
PhCOCl
–
PhOMe
79.7
66.5
28.8
57.9
55.1
86.9
71.8
28.5
76.5
48.3
66.1
55.6
27.1
57.7
29.2
43.1
29.6
3.6
82.3
71.8
29.8
58.1
55.7
87.4
72.6
29.7
79.6
58.4
67.7
57.1
27.5
58.8
32.8
57.6
31.3
6.4
83.5
68.4
58.3
28.6
55.7
88.2
62.4
78.8
32.3
58.5
62.3
56.7
54.5
28.6
28.7
56.5
30.1
14.5
4.8
PhCH COCl
2
n-C H COCl
5
11
c-C H COCl
6
11
PhCH=CHCOCl
PhCOCl
o-C H (Me)(OMe)
6
4
PhCH COCl
2
n-C H COCl
5
11
c-C H COCl
6
11
PhCH=CHCOCl
PhCOCl
o-C H (Br)(OMe)
6
4
PhCH COCl
2
n-C H COCl
5
11
c-C H COCl
6
11
PhCH=CHCOCl
PhCOCl
p-C H (Me)(OMe)
6
4
PhCH COCl
2
n-C H COCl
5
11
c-C H COCl
16.1
10.4
31.4
24.6
–
18.7
12.5
26.3
25.4
–
6
11
PhCH=CHCOCl
PhCOCl
11.8
31.7
25.3
–
p-C H (Br)(OMe)
6
4
PhCH COCl
2
n-C H COCl
5
11
c-C H COCl
PhCH=CHCOCl
–
–
–
–
–
–
6
11
Reagents and conditions: benzene derivatives: 2 mmol, acylating reagents: 6 mmol, [Cp*Mo(CO) ] :
3
2
1
–
0 mol%, o-chloranil 40 mol%, 80 °C, 24 h
no product detected
Complexes 1–3 all proved to be capable of catalyzing
Friedel–Crafts acylation reactions. The yields were found to
vary with the diꢁerent catalysts used, as indicated in Table 3.
The catalytic results for the three complexes were all basi-
cally similar; the diꢁerent substituents have only a small
inꢀuence on the catalytic behavior. Since these substituents
were not directly coordinated with the metal atoms, their
electronic and steric eꢁects are probably limited. The aryl
products were obtained in moderate yields, with high para-
selectivities. The pattern of results suggests that the reac-
tions proceed by an electrophilic substitution mechanism.
Benzoyl chloride, phenylacetyl chloride, cyclohexyl chlo-
ride, and cinnamyl chloride could all be used as acylating
reagents in these reactions. Comparing 2-methyl anisole as
the substrate and catalytic yield as standard, the order of
reactivity of the diꢁerent acylating reagents was found to be:
benzoyl chloride > phenylacetyl chloride > cyclohexanoyl
chloride > cinnamyl chloride > hexanoyl chloride.
Conclusions
Reactions of substituted tetramethylcyclopentadienes with
Mo(CO) (CH CN) provided a series of substituted tetra-
3
3
3
methylcyclopentadienyl dinuclear molybdenum carbonyl
complexes. Friedel–Crafts reactions of aromatic compounds
with a variety of acylation reagents showed that complexes
1–3 all have catalytic activity. Benzoyl chloride, phenyla-
cetyl chloride, cyclohexyl chloride, and cinnamyl chloride
could all be used as acylating reagents in these aromatic
1
3

Transition Metal Chemistry
electrophilic substitution reactions. Compared with tradi-
tional catalysts, the present system has several practical
advantages: lower amounts of catalysts, mild reaction con-
ditions, high selectivity, and ease of use. To elucidate the
reaction mechanism and expand the synthetic utility of these
catalysts, further studies are currently in progress.
16. Barbero M, Cadamuro S, Dugghera S, Magistris C, Venturello P
(
2011) Org Biomol Chem 9:8393
1
7. Jha A, Garade AC, Shirai M, Rode CV (2013) Appl Clay Sci
7
4:141
18. Prakash SGK, Fogassy G, Olah GA (2010) Catal Lett 138:155
19. Ma ZH, Lv LQ, Wang H, Han ZG, Zheng XZ, Lin J (2016) Transit
Met Chem 41:225
2
2
2
2
2
0. Li Z, Ma ZH, Wang H, Han ZG, Zheng XZ, Lin J (2016) Transit
Met Chem 41:647
Acknowledgements The authors gratefully acknowledge the ꢂnan-
1. Ma ZH, Zhang XL, Wang H, Han ZG, Zheng XZ, Lin J (2017) J
Coord Chem 70:709
cial support from the National Natural Science Foundation of China
(
No. 21372061), the Hebei Natural Science Foundation of China (No.
2. Li ZW, Ma ZH, Li SZ, Han ZG, Zheng XZ, Lin J (2017) Transit
Met Chem 42:137
B2017205006), and the Key Research Fund of Hebei Normal Univer-
sity (No. L2017Z02).
3. Ma ZH, Li ZW, Qin M, Li SZ, Han ZG, Zheng XZ, Lin J (2017)
Chin J Inorg Chem 33:1074
4. Zhang N, Ma ZH, Li SZ, Han ZG, Zheng XZ, Lin J (2017) Chin
J Inorg Chem 33:1497
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